Several aspects of the stimulus effects of drugs will be investigated in albino rats using a newly developed technique of body restraint. The animals will learn to make differential responses that require minimal muscular movement (lateral turning of the head in opposite directions). Initially the discrimination will be learned after pentobarbital or saline is administered intraperitoneally but new animals will learn under optimal conditions of a brief, 15-second interval after intravenous infusion of the drug or control fluid. Subsequent experiments will apply the technique to other conditions, including longer time intervals after i.p. or p.o. administration. In another series of studies, animals will be trained to discriminate between chlordiazepoxide and pentobarbital in an attempt to identify differential effects of these similar drugs. Other rats will learn to associate differential conditional stimuli (auditory or visual) with the differential drug conditions by Pavlovian classical conditioning. Differential responses by the animals will select between the two conditional stimuli, thus providing quantitative measurements of the reinforcing or aversive effects of the drugs.